Effectiveness of spinosad against seven major stored‐grain insects on corn

Abstract In January 2005, the United States Environmental Protection Agency registered spinosad as a stored grain protectant. No referenced data on the efficacy of spinosad on corn in suppressing major stored‐grain insects have been published. In this paper, we evaluated the efficacy of spinosad against seven major stored‐grain insects on shelled corn in the laboratory. Insect species tested were the red flour beetle, Tribolium castaneum (Jacquelin duVal); rusty grain beetle, Cryptolestesferrugineus (Stephens); lesser grain borer, Rhyzopertha dominica (F.); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); rice weevil, Sitophilus oryzae (L.); maize weevil, Sitophilus zeamais (Motschulsky); and Indian meal moth, Plodia interpunctella (Hübner). Corn kernels were treated with spinosad at 0, 0.1, 0.5, 1, and 2 active ingredient (a.i.) mg/kg for controlling the seven species. Beetle adults or P. interpunctella eggs were introduced into each container holding 100 g of untreated or insecticide‐treated corn. The seven insect species survived well on the control treatment, produced 28 to 336 progeny, and caused significant kernel damage after 49 days. On spinosad‐treated corn, adult mortality of C. ferrugineus, R. dominica, O. surinamensis, S. oryzae , and S. zeamais was > 98% at 1 and 2 mg/kg after 12 days. Spinosad at > 0.5 mg/kg completely suppressed egg‐to‐larval survival after 21 days and egg‐to‐adult emergence of P. interpunctella after 49 days, whereas 16% T. castaneum adults survived at 1 mg/kg after 12 days. Spinosad at 1 or 2 mg/kg provided complete or near complete suppression of progeny production and kernel damage of all species after 49 days. Our results indicate that spinosad at the current labeled rate of 1 mg/kg is effective against the seven stored‐grain insect pests on corn.